Tap-changing-underload equipment



Api-il 25, 1933. F, SNYDER 1,905,249

TAP CHANGING UNDERLOAD EQUIPMENT Filed Dec.` 12, 195o SEQUENCE OFOPER/1770 mw/2s 567os9 /l 1a /a 7? le 'ATTORNEY Patented Apr. 25, 1933UNITED STATES 'PATENT OFFICE FRANKLIN L. SNYDER, OF SHARON,PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY,A CORPORATION OF PENNSYLVANIA.

TAP-CHANGING-UNDERLOAD EQUIPMENT Application led December 12, 1930.Serial No. 501,871..

- My invention relates to tap-changing equipment for transformers andmore particularly to the tap-changing under-load equipment fortransformers wherein a relatively large number of tap positions aredesired.

With many forms of tap-changingequipment used inthe past, the number ofregulating voltage steps are limited because it is 4diiicult orimpractical toprovide alarge number of tap connections to the maintransformer winding. l

An object of my invention is to provide a tap-changing equipment havinga large number of tap-changing positions that are obtainable with acomparatively few tapchanging switches.

The invention, with additional objects and advantages thereof, will bebetter understood from the following description, when read inconjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic view of circuits and apparatus illustratingone preferred embodiment of my invention, and

Fig. 2 is a portion of a sequence chart showing the sequence ofoperation of the several switches .illustrated in Fig. 1. l

Referring to the drawing, a transformer, which is illustrated as anauto-transformer 41,

is provided for supplying power to a load, such as the furnacetransformer 5. The autotransformer is provided with a primary r winding2 that is connected to power-circuit conductors 3 and 4, Vand suppliesenergy to the primary winding 29 of the transformer 5 by means ofconductors 6 and 7. The conductor 7 is connected to the winding 2through a preventive auto-transformer 8 and through an intermediatetap-changing transformer 17 and an intermediate auto-transformer 22.Switches 9, 10, 11, 12, 13 and 14 of tap-changer 15 are connected to tappoints on the winding` 16 of the intermediate transformer 17. Reversingswitches 1.8 and 19 are provided between one end of the winding 16 andopposite ends of the auto-transformer 22 f and are effective to connectthe winding 1G across the one or the other of the windings l2O or 21which comprise the intermediate auto-transformer 22. From theintermediate auto-transformer 22, the circuit to the transformer 1 iscompleted through two of the operating switches 23, 24, 25, 26 and 27 oftap-changer 28. i

The reversing switches 18 and 19 are effective to conne'ct the portion20 or the portion 21 of the transformer 22 to the winding 16. A voltagewill, therefore, be applied to the winding 16 that is one half thevoltage between adjacent tap-changing switches 23 to 27, inclusive. Theseveral switches are operated in accordance with the sequence ofoperation shown in the chart in Fig. 2.

The numerals reading from left to right across thetop of the chart ofFig. 2 indicate controller positions having definite voltageratiovalues. The numbers reading from top to bottom at the left of the chartrefer to the correspondingly numbered switches shown in Fig. 1. Thecircles in the chart of Fig. 2 indicate that theswitchesdesignated bythe numbers at the left of the chart are closed on the controllerpositions indicated at the vtop of the chart. l

In the controlled position 1 of Fig. 2, it will be noted that switches 9and 14 of tap-changer 15, reversing switch 18, and switches 23 and 24 ofthe tap changer 28 are closed. Switch 14, in its closed position, causesthe windings of the preventive auto-transformer 8 to neutralize eachother, and, in effect, connects the conductor -7 directly to one end ofthe winding 16 through the switch 9. With the reversing switch 18closed, a voltage, corresponding to that of the winding 20 of theintermediate auto-transformer 22, is impressed upon the winding 16. Thevoltage o f lthe primary windings 2O and 21 of the autotransformer 22 isthe same as that impressed between the taps operated by switches 23 and24 of the tap changer 28.

In position 2 of the controller, switch 14- 8 is connected to differentpairs of adjacent taps of the intermediate transformer 17 to vary thevoltage applied to the furnace transformer. The opening of switch 14 andthe closing of switch 10 changes the voltage one step and connects thepreventive auto-transformer 8 between the switches 9 and 10, thus, ineffect, connecting the conductor 7 to a point on the winding 16 that ismidway between the two taps connected to switches 9 and 10. The switches23 and 24 remain closed in controller position 2. In controller position3, switch 10 of tap-changer 15 remains closed, switch 9 is opened andswitch 14 is closed. This changes the taps another step, and a voltageon the mid-tap of the preventive auto-transformer 8'is obtained thatcorresponds to that of tap 10. The switches 23 and 24 remain closed, asin controller position 2.

It will be noted that, during the first nine controller positions, thereversing switch 18 has remained closed, and the reversing switch 19 hasremained open. On the controller position 9, the conductor 7 isconnected, through closed switches 14 and 13, to the middle point of thewinding 22. In the transition from the controller position 9 to thecontroller position 10, an intermediate step 9 appears, wherein theswitch 18 is opened and the switch 19 is closed. This intermediate stepdoes not produce a voltage change, since the connection of the conductor7 to the winding 22 is not altered thereby. During the operation of thecontroller from position 9 to 17, inclusive, the tap-changer 15 reversesthe sequence of steps from position 1 to 9, inclusive. At the controllerposition 17, the conductor is connected to the winding 2 through closedswitches 14, 9, 19 and 24. Switch 23 is then opened and switch 25closed, and the tap-changer 15 repeats a similar operation, as describedabove.

When the switches in the tap-changer 15 have been operated through theirsequence of steps, the connection of the winding 16 to the winding 2 ischanged either by operation of one of the reversing switches 18 and 19or by one of the switches of the tap-changer 28, depending upon whichstep of the complete series is to be made.

The reversing switches 18 and 19 serve to connect one end of the winding16 to one of the tap switches 23 to 27, inclusive, the other end of thewinding 16, being, in effect, connected to a point in the winding 2 thatis mid-way between the two switches of the groups 23 to 27 inclusive,that is closed. In a similar manner, the complete sequence of operationof the switches may be followed by further reference to the chart shownin Fig. 2. All switches may be either automatically or manuallyoperated, as desired.

From the above discussion, it may be seen that I have devised means forvarying the voltage ratio of a transformer that is easily constructedand operated. My described tapchanging system provides a large number ofvoltage steps with the use of a relatively small number of tap-changingswitches.

Although I have shown and described a certain specific embodiment of myinvention, I am fu ly aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and bythe spirit of theappended claims.

I claim as my invention:

1. In a tap-changing system for transformers, a primary power circuitcomprising a pair of conductors, a transformer winding energized fromsaid power circuit and provided with a plurality of tap connections, anintermediate transformer energized from said first-named winding, and atap-changing transformer energized from said intermediate transformer,tap-changing switches for varying the connection of said intermediatetransformer to said first-named winding, reversing means for changingthe connection of tap-changing transformer to said lintermediatetransformer, and a plurality of tapchanging switches for varying theconnection of said tap-changing transformer to a power-circuitconductor.

2. In a tap-changing system for transformers, a transformer wmdingconnected to a power circuit and provided with a plurality oftap-changing switches, a pair of intermediate transformers connected tosaid tapchanging' switches, means for changin the polarity of one saidintermediate trans ormers with respect to the other, the last-namedintermediate transformer being provided with a plurality of tapconnections, and means for varying the tap connections of saidlast-named intermediate transformer.

3. In a transformer-voltage-ratio-control system, a power circuit and atransformer winding energized thereby, two intermediate transformersconnected in cascade, means for changing the polarity of one of saidintermediate v transformers with respect to the other, a plurality oftap-chan ing switches connected to said first-name transformer windingfor connecting one of said intermediate transformers between selectedpoints thereon, and voltage-ratio control means at tached to the otherof said intermediate transformers, said voltage-ratio control meanscomprising a plurality of tap-changing switches and a controlledpreventive autotransformer, said reventive auto-transformer beingconnecte to said power circuit.

In testimony whereof, I have hereunto subscribed my name this 4th day ofDecember FRANKLIN L. SNYDER.

